U.S. Pat. No. 3,912,693 discloses a photopolymerization method for preparing diallyl quaternary ammonium/maleic acid copolymers.
U.S. Pat. No. 4,640,793 discloses the use of admixtures containing carboxylic acid/sulfonic acid polymers and phosphonates as scale and corrosion inhibitors.
EPO Pat. Appln. No. 84102890.5 discloses copolymers of maleic acid and an adduct of an oxyalkylene and allyl alcohol, and the use thereof for scale inhibition.
Japanese No. 57-084794 discloses the use of copolymers of acrylic acid and allyl polyethylene glycol as scale inhibitors.
U.S. Pat. No. 4,297,237 discloses the use of polymaleic anhydride and polyphosphates as corrosion inhibitors, and U.S. Pat. Nos. 3,810,834, 3,963,363 and 4,089,796 disclose methods of treating the water of an aqueous system with hydrolyzed polymaleic anhydride to inhibit scale formation.
U.S. Pat. Nos. 2,723,956, 3,289,734, 3,292,152, 3,578,589 and 3,715,307 relate to the use of polymaleic anhydride and copolymers thereof as scale control agents.
U.S. Pat No. 3,965,027 discloses the use of certain amine adducts of polymaleic anhydride as scale and corrosion inhibitors.
European patent application 84301450.7 discloses carboxylic acid/sulfonic acid copolymers in combination with organic phosphonates as scale inhibitors.
U.S. Pat. Nos. 4,176,059, 4,217,216, and 4,246,030 disclose the use of molybdate compositions for corrosion inhibition.
However, none of the prior art references described above in any way suggest the use of the instant polymers as scale control agents.
Many commercial waters contain alkaline earth metal cations, such as calcium, barium, magnesium, etc., and anions such as carbonate, sulfate, oxalate and/or phosphate. When the concentrations of these anions and cations are sufficiently high, their reaction products become insoluble and precipitates form until the solubility limits are no longer exceeded. These precipitates are alkaline earth metal scales. For example, when the concentrations of calcium ion and the any of the above mentioned anions are sufficient to exceed the solubility limitations of the calcium-anion reaction products, a solid phase of calcium scales will form as a precipitate.
Solubility product concentrations are exceeded for various reasons, such as evaporation of the water phase, change in pH, pressure, or temperature, and the introduction of additional ions which can form insoluble compounds with the ions already present in the solution. As these reaction products precipitate on heat transfer surfaces in contact with aqueous streams, they form scale. The scale prevents effective heat transfer, interferes with fluid flow, facilitates corrosive processes, and harbors bacteria. Scale is an expensive problem in many industrial water systems, causing delays and shut downs for cleaning and removal. Alkaline earth metal scales commonly form on the metallic surfaces of apparatuses used for thermal treatment of aqueous solutions and suspensions. By alkaline earth metal scales, we mean scales including but not limited to calcium carbonate, calcium oxalate, magnesium carbonate, calcium phosphate, calcium sulfate, and barium sulfate. These scales frequently form in the tubes of heat exchangers and on other heat exchange surfaces.
In the past, alkaline earth metal scale inhibition has been facilitated by the use of anionic polyelectrolytes such as polyacrylates, polymaleic anhydrides, copolymers of acrylates and sulfonates, and polymers of sulfonated styrenes. However, over the past few years, high pH and/or non-chromate corrosion treatment programs have become increasingly important. The use of corrosion inhibitors such as zinc salts and/or phosphates requires that an effective scale inhibitor be used to prevent the deposition of the reaction products formed when the added inhibitors combine with the ions present in the water. Also, an effective inhibitor can increase the solubility of the corrosion inhibitors, and thus improve corrosion protection.
The deposition of iron oxide on surfaces is another severe problem in industrial cooling water systems. For example, the prevention of iron oxide precipitation is essential in nuclear power plants.
In the paper industry, the formation of scales such as barium sulfate and calcium oxalate on metal surfaces causes processing problems. These scales form rough, hard, tenacious deposits which can cause reduced stock flow, formation problems and machine down time due to the generation of fiber twists and the sloughing-off of biological debris. Sub-deposit corrosion can also be a major problem due to the activity of sulfate-reducing bacteria.
Accordingly, the need exists for an inexpensive, efficient method and composition for preventing the formation of deposits on metallic surfaces in contact with water by inhibiting the formation of scales and/or by dispersing scale-forming compounds.
The instant inventors have discovered a method for controlling scale deposition and/or dispersing scale-forming compounds in aqueous systems using maleic acid/quaternary ammonium-type polymers. While such polymers alone are effective inhibitors, other common scale and/or corrosion inhibitors may enhance their performance under certain conditions.
The instant polymers are especially effective agents for controlling calcium scales, particularly calcium oxalate.